Perpetual Malcontent

A person who is only truly happy when he/she is upset. The inability to experience any or all of the following: happiness, laughter, joy, comradery. A tendency toward feeling bitter, scorn, spite, wrath, vengeful. See also killjoy and buzzkill.

A Perpetual Malcontent is one who complains about the quality of free food. A perpetual malcontent is critical of an event everyone else enjoyed.